Different grace periods for individual transactions, i.e. individual disbursements posted on a revolving credit account.
It is a standard in the UK that different credit card transactions will have their own interest free periods.
For instance, online purchases may be interest free for the first 50 days, but then subject to a rate of 19.5% per year until the transaction is repaid. Transactions posted on different dates would therefore become subject to interest on different dates as well, such as the following:
01.07.20: TxA, £50 online purchase (TxA day 0 = 0%)
10.07.20: TxB £20 online purchase (TxA day 9 = 0%, TxB day 0 = 0%)
21.08 20: TxA day 51 = 19.5%, TxB day 42 = 0%)
Please note that the grace period and rate may also change based on the transaction type. For instance, ATM withdrawals may have a higher rate and no grace period.